Variable buoyancy systems are commonly employed in salvaging objects from the ocean or positioning and recovering oceanographic instrumentation. These buoyancy systems may take several different forms, such as lift bags or ballast tanks. Historically, high pressure air tanks have been utilized for deballasting such buoyancy systems. More recently various substances have been reacted to generate a gas for deballasting the systems. Hydrazine is commonly reacted to generate a gas, and has been found highly satisfactory for raising large objects from the ocean bottom. However, hydrazine is not cost effective when smaller objects are to be salvaged. Gas generated by reacting metallic hydrides is considerably more cost effective in raising smaller objects, however, prior art gas generators using metallic hydrides could not be controlled sufficiently to perform their intended job function. The specific problem with prior art gas generators utilizing metallic hydrides is in the starting and the stopping of the reaction.